Toxic Air Pollutants

Nature and Sources:
Toxic air pollutants are those pollutants known or suspected to cause cancer
or other serious health effects, such as birth defects or reproductive
effects. Examples of toxic air pollutants include dioxins, benzene, arsenic,
beryllium, mercury, and vinyl chloride. The Clean Air Act currently lists
188* toxic air pollutants to be regulated by EPA. They are emitted from
all types of sources, including motor vehicles and stationary sources,
such as manufacturing plants. ( * Captrolactam was
recently removed from the list of toxic air pollutants, which originally
numbered 189.)

Control of toxic air pollutants differs in focus from control of the
six principal pollutants for which EPA has established national air quality
standards (discussed earlier). For the six principal pollutants, a variety
of control strategies are used in geographic areas where national air quality
standards have been violated. In contrast, for toxic air pollutants, EPA
has focused on identifying all major industrial sources that emit these
pollutants and developing national technology-based performance standards
to significantly reduce their emissions. The objective is to ensure that
major sources of toxic air pollution are well controlled regardless of
geographic location.

EPA's toxic air pollutant program and the NAAQS program complement each
other. Many toxic air pollutants are emitted in the form of particulates
or as VOC. Control programs to meet the NAAQS for ozone and PM-10 also
reduce toxic air pollutant emissions. Likewise, emission requirements under
the toxic air pollutants program can significantly help achieve the NAAQS
for ozone and PM-10. For example, EPA's final toxic air pollutant regulation
for organic chemical manufacturing is expected to reduce VOC emissions
(which form ground-level ozone or smog) by an amount equivalent to removing
millions of cars from the road.

The toxic air pollutant program is especially important in reducing
emissions at or near industrial locations and in controlling pollutants
that are toxic even when emitted in small amounts. Companies handling toxic
chemicals are required by EPA to develop plans to prevent accidental releases
and to contain any releases in the event they should occur.

Health and Environmental Effects:
At sufficient concentrations and exposure durations, human health effects
from toxic air pollutants can include cancer, poisoning, and rapid onset
of sickness, such as nausea or difficulty in breathing. Other less measurable
effects include immunological, neurological, reproductive, developmental,
and respiratory effects. Toxic air pollutants may also be deposited onto
soil or into lakes and streams, thereby affecting ecological systems and
eventually human health through consumption of contaminated food (mainly
freshwater fish).

Trends In Toxic Air Pollutants:
EPA will soon begin using the National Toxics Inventory (NTI) to track
nationwide emissions trends for toxic air pollutants listed in the Clean
Air Act. NTI contains information on toxic emissions in 1990 of approximately
8.8 billion pounds. As illustrated in the chart below, NTI includes emissions
from large industrial or "point" sources, smaller stationary sources called
"area" sources, and mobile sources. NTI builds on emissions data from EPA's
Toxic Release Inventory, which reflects about half the total emissions
from large industrial point sources and about 14 percent of national total
emissions.

According to National Toxics Inventory data, area sources account
for 31 percent of U.S. toxic emissions, mobile sources account for
39 percent, and point sources account for 30 percent.

Selected VOC Concentration
ChangesFrom PAMS Sites (Summer 1994-1995)

These substances have high ozone
forming potential and/or they are toxic

Pollutant

Number of Sites

Median % Change

2,2,4-Trimethylpentane

17

-23

Acetaldehyde

6

-14

Benzene

19

-38

Ethylbenzene

17

-23

Formaldehyde

6

+4

M/P-Xylene

14

-21

N-hexane

17

-8

O-xylene

17

-18

Styrene

17

-17

Toluene

17

-23

As of October 1996, EPA has issued air toxics standards for 47 source categories,
such as chemical plants, oil refineries, aerospace manufacturers, and steel
mills, as well as area sources like dry cleaners, commercial sterilizers,
secondary lead smelters, and chromium electroplating. When these standards
are fully implemented, toxic emissions from stationary sources should be
reduced by approximately 35 percent. Toxic emissions from point sources
have already declined, a trend that is expected to continue as the result
of emissions standards. By the year 2005, EPA projects that the toxic air
pollutant program will reduce toxic emissions by 75 percent. Because controls
for toxic air pollutants also reduce VOC and PM-10 emissions, over the
next 10 years, the program should realize reductions in VOC and PM-10 emissions
of more than 4 billion pounds per year.

Preliminary analysis of specific VOC measured in urban locations classified
as "serious," "severe," or "extreme" ozone nonattainment (PAMS network
- see Ozone section) indicate
that ambient concentration levels of certain toxic VOC appear to be declining.
For example, as illustrated in the above table, benzene levels showed a
significant decline between 1994 and 1995 (approximately 38 percent), possibly
as a result of the use of reformulated gasoline in those areas. It should
be noted that PAMS measurements have only been taken for 3 years and that
continued efforts in the PAMS program are expected to provide more confidence
in evaluating the long-term trends of benzene and other toxic VOC.

This document is provided for historical
purposes only. The most recent version can be found at AIRTrends